In the Ma’aza territory, north of the road between Quseir and Qift, such wet years are reported, among others, 1928–1932, 1949–1951, 1956–1958, and 1977–1985. Seven cloudbursts are recorded by Springuel over the past 15 years in the southern part of the Eastern Desert. The most recent one was in November 1996 and fell over much of the Western and Eastern deserts. However, winter rains mostly result in limited amounts of rainfall. Because the main rain-producing winds come from a northeasterly direction, rainfall is concentrated on the northeastern sides of the mountains. This orographic influence of the Red Sea coastal mountains results in a comparatively well-developed flora on the slopes. The Elba area in particular, located some 260 km south of Berenike, catches much water in this way, and a unique Sudanese flora characterizes its slopes. Most mountain slopes north of the Gebel Elba are, however, almost barren. Especially during nighttime, the evaporation is minimal, and much water sinks into the coarse wadi sand. Some water is caught in rock depressions and is used by animals and humans as a source of drinking water. Even if such rocky clefts are difficult to inspect by eye, the presence of water can easily be checked by throwing a piece of stone. For the Eastern Desert it should thus be realized that the almost-barren orographic relief affects principally the redistribution of rainfall. As a result, the water supply of wadi branches is actually much more than what is calculated on the basis of the mean annual precipitation. This concentration of water is also supported by the presence of impervious surface crusts,blueberry plant pot which are found in hyperarid regions in particular and are virtually water resistant .
Water that penetrates deep into the wadi escapes evaporation and will be available for plants with deep taproots. The amount of water that can sink into the ground will largely depend on the texture of the soil, in which penetration and the coarseness of the soil texture are positively correlated. For this reason, sandy soils offer better water supplies in dry regions than clay soils . Silty depressions are an exceptional case as the concentration of the water may compensate the high field capacity, which hinders water penetration. Groundwater will be drained by an underflow toward the Red Sea or the Nile. Such an underflow was probably used by the Romans in the watering station Kalalat as a source of water for the inhabitants of Berenike. The persistence of this water fl ow is demonstrated by the permanent presence of slow running water in a narrow gorge of Wadi Shenshef, even when preceding winter rains have not been recorded. From the Greek period onward, the groundwater in Arabia, stretching from Kuwait through eastern Arabia to Bahrain, has been exploited via a network of aquifers, which could be tapped for drinking water and irrigation .Atmospheric humidity is an important source of water for plants growing in the Red Sea coastal zone. Evaporation of seawater during daytime replenishes the water content of the air. This water partly condenses again as the temperature of the air sufficiently drops during winter and early spring. Considering the fact that air temperature is lowest just before sunrise, morning dew may therefore be responsible for damp soils. Unlike precipitation, morning dew is a much more steady water source for plants. Referring to agricultural practices in Bactria, Africa, and Cyrene, Pliny even states that crops depend on the dew fall at night for their nourishment. Also Theophrastus emphasizes the contribution of dew to plant growth in regions with no rainfall, including Egypt.
According to Jabbur , who studied the bedouin life in the Syrian Desert, there is so much dew on plants in spring, that some women collect the water in their water skins. This atmospheric humidity is of value for both the fl at coastal plain adjacent to the Red Sea proper and the mountains, which intercept the clouds blown inland. Especially high mountain massifs may receive considerable amounts of rain in this way. This also explains the presence of several mosses and ferns on the higher levels of the Gebel Elba . Fertilization of these plants is only possibly under moist-to-wet conditions.The adaptation of desert plants to water stress is diverse. Several principles can be distinguished and specific combinations of such principles may find their expression in desert plants. One possible adaptation that has arisen by natural selection is the storage of water in leaves, stems, or roots. Such plants are called succulents and are adapted to arid habitats as well as to saline environments. Succulent plants that grow in the Eastern Desert, including the environment of Berenike, are Suaeda monoica Forssk. ex J. F. Gmel, Halopeplis perfoliata Bunge ex Asch., and Aizoon canariense L. A good example of a halophytic succulent is Zygophyllum coccineum, which has swollen stems and leaves and is able to abort part of its leaves and even young shoots to prevent excessive water loss. Other plants have leaves with xeromorphic features. They are called xerophytes and are, by definition, adapted to arid regions. A common feature is the reduction in size and/or number of the leaves, as can be observed by Crotalaria aegyptiaca Benth. and Moringa peregrina Fiori. An extreme example of leaf reduction is demonstrated by Tamarix aphylla H. Karst, a shrub that has only sheath-like leaves. Another way of drought survival is shortening the life cycle. Annual plants that take advantage of the availability of water independent of the season, being either a rain shower or a damp period caused by dewfall, are called ephemerals.
They include succulents, such as Zygophyllum simplex L.; nonsucculents, including grasses such as Aristida funiculata Trin. & Rupr.; and nongrasses such as Lotononis platycarpa Pic. Serm. Such plants can survive by a quick absorption of the rainwater and dew. Some of them have reasonably long roots, such as species of Aristida, whereas other plant species have only very small and shallow root systems, such as stunted but flowering specimens of Triraphis pumilio R. Br., Eragrostis ciliaris R. Br., and Coelachyrum brevifolium Hochst. & Nees. These plants were frequently found in the environment of Berenike and Shenshef. Some plants may develop temporarily so-called rain or extension roots, which grow in the upper part of the soil and absorb the water from a rain shower or dew . Perennials may also be have as ephemerals. Conversely, some species, such as Zygophyllum simplex, that normally behave as ephemerals, can prolong their life span under favorable conditions . They are as resistant to drought as a seed. Plants that obtain their water directly or through the capillary fringe from the groundwater are called freatophytes. Because in most cases groundwater is only available at considerable depths, freatophytes are predominantly perennial species that are able to develop deeply penetrating taproots. Regeneration of freatophytes will be especially successful during years with heavy showers, resulting in a moist soil from the surface down to the water table over a considerable time span. During this period, long taproots must grow to the water table. As soon as this is reached, the plants will have become independent of the unpredictable rainfall and can survive in an apparent unfavorable environment. A good example of a desert freatophyte is the twisted acacia , which may have a taproot of more than 40 m. Owing to its deep, penetrating root,plastic gardening pots this tree is capable of growing in the fringe of wadi branches. Their presence is even indicative of the many wadi branches that dissect the fl at coastal plains along the Red Sea. The growth of the root starts soon after germination. A seedling under a full-grown tree in Wadi Shenshef of only 2 cm high could be dug out to a length of 25 cm before its fragile root broke off. Examples of herbaceous species with long roots are Aerva javanica Juss. ex Schult., and Aizoon canariense L. Some plants, such as the Nile tamarisk , are capable of initiating condensation of atmospheric moisture by means of special hygroscopic salt crystals under conditions of high humidity . For this reason, drops of water on the surface of the Nile tamarisk taste rather salty. The water condensation is triggered when the humidityof the air exceeds 76 percent . Like dew deposition on the plant surface, which depends on a lower plant surface temperature in relation to the dew point temperature of the adjacent air, this salty water drips from the plant and can be absorbed by the shallow roots. The effectiveness of this self-induced sprinkling is evidenced by the many imprints of raindrops in the damp soil beneath such excretive plants.
The availability of water is, however, no guarantee for the presence of desert plants. This is especially true of regions that do not profit from the dewfall. Here, the irregularity of rainfall is at odds with the presence and longevity of seeds in the soil. Seed banks in desert soils are characterized by a concentration of seeds in the upper 2 cm of soil, with a high degree of spatial heterogeneity and a great seasonal and annual variability. Seeds tend to be concentrated in depressions where water collects and in wind shadows, such as below established plant species . As dispersal distances are generally short, a specific type of ephemeral vegetation may exist for several years . Isolated spots that are completely dependent on unpredictable showers may lack a viable seed bank, and consequently no vegetation will develop after rainfall .The major phytogeographical districts that are distinguished in Egypt are: the Mediterranean coastal strip, the Nile region, the deserts, the mountainous region of the Sinai proper, the oases, and the Sahelian scrub region in and around Gebel Elba . A further division is possible with respect to the Mediterranean area, the Nile Valley, and the deserts . Because the desert vegetation is of prime interest, only the division of the desert vegetation will be discussed in more detail. The Egyptian desert is divided by the Nile Valley into the Western or Libyan Desert and the Eastern or Arabian Desert. Additionally, the Nubian Desert is distinguished, being present on both sides of the Nile south of Aswan. Both the Libyan and Nubian deserts are flat and have several large depressions . On the eastern side of the Nile, three different deserts are distinguished. The Isthmic Desert is located south of the Mediterranean coastal strip on both sides of the Suez Canal. South of this desert, fringed by the Nile and the Gulf of Suez, lies a small desert area consisting of limestone mountains called the Galaga Desert. The Eastern Desert is the third one in the row and extends southward from about lat 26° N to the Gebel Elba region . This large desert is characterized by rugged, igneous mountains that run parallel to the Red Sea on the east side and a rocky plateau on the west side. The Red Sea mountains are dissected by a web of branched wadis that drain off into either the Nile or the Red Sea. Although a detailed labeling of the distribution of the complete Egyptian flora is presented by Täckholm , including a dichotomy between the northern and southern part of the Eastern Desert, which coincides with the territories of the Ma’aza and Ababda nomads, respectively, it has not been used in this study because it is too out-of-date due to many taxonomical revisions and corrections of geographical distribution records during the last decades. Between the mountains and the Red Sea there is a gently sloping coastal plain. Near Berenike this plain is only 8 km wide, but elsewhere it can extend as far as 35 km. This fl at plain is dissected by many wadis draining off into the Red Sea, and its flora differs so much from the flora of the mountainous areas that it represents a separate phytogeographical district. The Egyptian flora comprises almost 2,100 plant species. The distribution of these species over the major phytogeographical regions is presented in Figure 2.8. The analysis is based on the checklist of the Flora of Egypt , the Flora of Egypt and the Key to the Egyptian Grasses .